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diff mercurial/help/internals/wireprotocol.txt @ 37485:0b7475ea38cf

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wireproto: port heads command to wire protocol v2 After much thought and consideration, wire protocol version 2's commands will be defined in different functions from the existing commands. This will make it easier to implement these commands because it won't require shoehorning things like response formatting and argument declaration into the same APIs. For example, wire protocol version 1 requires that commands declare a fixed and ordered list of argument names. It isn't really possible to insert new arguments or have optional arguments without breaking backwards compatibility. Wire protocol version 2, however, uses CBOR maps for passing arguments. So arguments a) can be optional b) can be added without BC c) can be strongly typed. This commit starts our trek towards reimplementing the wire protocol for version 2 with the heads command. It is pretty similar to the existing heads command. One added feature is it can be told to operate on only public phase changesets. This is useful for making discovery faster when a repo has tens of thousands of draft phase heads (such as Mozilla's "try" repository). The HTTPv2 server-side protocol has had its `getargs()` implementation updated to reflect that arguments are a map and not a list. Differential Revision: https://phab.mercurial-scm.org/D3179
author Gregory Szorc <gregory.szorc@gmail.com>
date Wed, 28 Mar 2018 14:55:13 -0700
parents afcfdf53e4b5
children 6847542bb8d7
line wrap: on
line diff
--- a/mercurial/help/internals/wireprotocol.txt	Wed Mar 28 10:52:40 2018 -0700
+++ b/mercurial/help/internals/wireprotocol.txt	Wed Mar 28 14:55:13 2018 -0700
@@ -1649,3 +1649,40 @@
 
 The server may also respond with a generic error type, which contains a string
 indicating the failure.
+
+Frame-Based Protocol Commands
+=============================
+
+**Experimental and under active development**
+
+This section documents the wire protocol commands exposed to transports
+using the frame-based protocol. The set of commands exposed through
+these transports is distinct from the set of commands exposed to legacy
+transports.
+
+The frame-based protocol uses CBOR to encode command execution requests.
+All command arguments must be mapped to a specific or set of CBOR data
+types.
+
+The response to many commands is also CBOR. There is no common response
+format: each command defines its own response format.
+
+TODO require node type be specified, as N bytes of binary node value
+could be ambiguous once SHA-1 is replaced.
+
+heads
+-----
+
+Obtain DAG heads in the repository.
+
+The command accepts the following arguments:
+
+publiconly (optional)
+   (boolean) If set, operate on the DAG for public phase changesets only.
+   Non-public (i.e. draft) phase DAG heads will not be returned.
+
+The response is a CBOR array of bytestrings defining changeset nodes
+of DAG heads. The array can be empty if the repository is empty or no
+changesets satisfied the request.
+
+TODO consider exposing phase of heads in response